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Summary - Conditionals

Combine if, if expression and when to write a day-of-week app.

Summary - Conditionals

In this summary you'll combine if, the if expression and when to build a day-of-week app. In previous lessons you learned:

  • condition checks with if
  • alternative branches with else and else if
  • returning values with the if expression
  • multi-way selection with when

We'll do two mini tasks: convert a day number to a name (when expression) and categorize a temperature (if expression).

Practice Find the day name with when

Write a fun main(). Assign 3 to val day. Write val name = when (day) { 1 -> "Monday" 2 -> "Tuesday" 3 -> "Wednesday" 4 -> "Thursday" 5 -> "Friday" else -> "Weekend" }. Print the result with println(name).

Starter code

Main.kt
fun main() {
    // Find the day name
}

Sample solution

Main.kt
fun main() {
    val day = 3
    val name = when (day) {
        1 -> "Monday"
        2 -> "Tuesday"
        3 -> "Wednesday"
        4 -> "Thursday"
        5 -> "Friday"
        else -> "Weekend"
    }
    println(name)
}

Expected output

Wednesday

Practice Categorize the temperature

Write a fun main(). Assign 25 to val temp. Write val category = if (temp >= 30) "Hot" else if (temp >= 15) "Mild" else "Cold". Print the result with println(category).

Starter code

Main.kt
fun main() {
    // Categorize the temperature
}

Sample solution

Main.kt
fun main() {
    val temp = 25
    val category = if (temp >= 30) "Hot" else if (temp >= 15) "Mild" else "Cold"
    println(category)
}

Expected output

Mild

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 Which is the most readable construct to compare a value against 5 options?

  • if/else if chain
  • Nested if
  • Ternary operator
  • when expression Correct answer

Explanation: when is the most readable for multi-way selection.

2 Complete the if expression

Question 
val category = if (temp >= 30) "Hot" ____ "Normal"
Answer 
val category = if (temp >= 30) "Hot" else "Normal"

Explanation: else gives the second branch's value in an if expression.

All lessons in Beginner

1 Kotlin basics

  1. What is Kotlin?
  2. Your first program
  3. The main function
  4. Comments
  5. String templates
  6. Summary - Kotlin basics

2 Variables

  1. val and var
  2. Type inference
  3. const
  4. lateinit
  5. by lazy
  6. Summary - Variables

3 Data types

  1. Integer types
  2. Floating-point types
  3. Boolean and Char
  4. String
  5. Any and Unit
  6. Summary - Data types

4 Project: Calculator

  1. Project design
  2. Add and subtract
  3. Multiply and divide
  4. Error handling
  5. Putting it together

5 Operators

  1. Arithmetic operators
  2. Assignment operators
  3. Comparison operators
  4. Logical operators
  5. Elvis operator
  6. Summary - Operators

6 Strings

  1. Creating strings
  2. String templates
  3. String methods
  4. substring
  5. split and replace
  6. Summary - Strings

7 Conditionals

  1. The if statement
  2. else and else if
  3. if expression
  4. when
  5. when expression
  6. Summary - Conditionals

8 Loops

  1. The for loop
  2. The while loop
  3. The do-while loop
  4. Range
  5. break and continue
  6. Summary - Loops

9 Project: Shopping cart

  1. Cart design
  2. Adding items
  3. Calculating totals
  4. Listing the cart
  5. Putting it together

10 Arrays

  1. Creating arrays
  2. Array access
  3. Array size
  4. Array loop
  5. Array methods
  6. Summary - Arrays

11 Lists

  1. Creating lists
  2. List operations
  3. List access
  4. List iteration
  5. List methods
  6. Summary - Lists

12 Maps and Sets

  1. Creating sets
  2. Set operations
  3. Creating maps
  4. Map operations
  5. Map iteration
  6. Summary - Maps and Sets

13 Functions

  1. Defining functions
  2. Return values
  3. Expression body
  4. Default parameters
  5. Named arguments
  6. Summary - Functions

14 Null safety

  1. Nullable types
  2. ?, !! and ?:
  3. let
  4. Null check
  5. lateinit
  6. Summary - Null safety

15 Project: To-do CLI

  1. Task model
  2. Adding tasks
  3. Listing tasks
  4. Completing tasks
  5. Putting it together

16 Advanced string operations

  1. Regex
  2. matches and find
  3. replace
  4. StringBuilder
  5. trim and pad
  6. Summary - Advanced strings

17 Enums

  1. enum class
  2. Enum values
  3. Enum properties
  4. when with enum
  5. Enum and range
  6. Summary - Enums

18 Exceptions

  1. try/catch
  2. throw
  3. finally
  4. try expression
  5. Custom exceptions
  6. Summary - Exceptions

19 Class basics

  1. class
  2. Constructor
  3. Properties
  4. Methods
  5. this
  6. Summary - Class basics

20 Beginner final

  1. Project design
  2. Classes
  3. Collections
  4. Error handling
  5. Putting it together